Journal Article

Probing the neutral fraction of the IGM with GRBs during the epoch of reionization

Matthew McQuinn, Adam Lidz, Matias Zaldarriaga, Lars Hernquist and Suvendra Dutta

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 3, pages 1101-1110
Published in print August 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI:
Probing the neutral fraction of the IGM with GRBs during the epoch of reionization

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We show that near-infrared observations of the red side of the Lyα line from a single gamma-ray burst (GRB) afterglow cannot be used to constrain the global neutral fraction of the intergalactic medium (IGM), , at the GRB's redshift to better than . Some GRB sightlines will encounter more neutral hydrogen than others at fixed owing to the patchiness of reionization. GRBs during the epoch of reionization will often bear no discernible signature of a neutral IGM in their afterglow spectra. We discuss the constraints on from the z= 6.3 burst, GRB050904, and quantify the probability of detecting a neutral IGM using future spectroscopic observations of high-redshift, near-infrared GRB afterglows. Assuming an observation with signal-to-noise ratio similar to the Subaru FOCAS spectrum of GRB050904 and that the column density distribution of damped Lyα absorbers is the same as measured at lower redshifts, a GRB from an epoch when can be used to detect a partly neutral IGM at 97 per cent confidence level ≈10 per cent of the time (and, for an observation with three times the sensitivity, ≈30 per cent of the time).

Keywords: galaxies: high-redshift; intergalactic medium; cosmology: theory

Journal Article.  8565 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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